diff options
Diffstat (limited to 'absl/base/config.h')
| -rw-r--r-- | absl/base/config.h | 43 |
1 files changed, 42 insertions, 1 deletions
diff --git a/absl/base/config.h b/absl/base/config.h index 58097b0d..94f7fcb5 100644 --- a/absl/base/config.h +++ b/absl/base/config.h @@ -56,6 +56,25 @@ #include <cstddef> #endif // __cplusplus +// ABSL_INTERNAL_CPLUSPLUS_LANG +// +// MSVC does not set the value of __cplusplus correctly, but instead uses +// _MSVC_LANG as a stand-in. +// https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros +// +// However, there are reports that MSVC even sets _MSVC_LANG incorrectly at +// times, for example: +// https://github.com/microsoft/vscode-cpptools/issues/1770 +// https://reviews.llvm.org/D70996 +// +// For this reason, this symbol is considered INTERNAL and code outside of +// Abseil must not use it. +#if defined(_MSVC_LANG) +#define ABSL_INTERNAL_CPLUSPLUS_LANG _MSVC_LANG +#elif defined(__cplusplus) +#define ABSL_INTERNAL_CPLUSPLUS_LANG __cplusplus +#endif + #if defined(__APPLE__) // Included for TARGET_OS_IPHONE, __IPHONE_OS_VERSION_MIN_REQUIRED, // __IPHONE_8_0. @@ -807,6 +826,29 @@ static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' || #define ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION 1 #endif +// ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL +// +// Prior to C++17, static constexpr variables defined in classes required a +// separate definition outside of the class body, for example: +// +// class Foo { +// static constexpr int kBar = 0; +// }; +// constexpr int Foo::kBar; +// +// In C++17, these variables defined in classes are considered inline variables, +// and the extra declaration is redundant. Since some compilers warn on the +// extra declarations, ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL can be used +// conditionally ignore them: +// +// #ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL +// constexpr int Foo::kBar; +// #endif +#if defined(ABSL_INTERNAL_CPLUSPLUS_LANG) && \ + ABSL_INTERNAL_CPLUSPLUS_LANG < 201703L +#define ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL 1 +#endif + // `ABSL_INTERNAL_HAS_RTTI` determines whether abseil is being compiled with // RTTI support. #ifdef ABSL_INTERNAL_HAS_RTTI @@ -868,5 +910,4 @@ static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' || #define ABSL_INTERNAL_HAVE_ARM_NEON 1 #endif - #endif // ABSL_BASE_CONFIG_H_ |